Plans to build the world's largest offshore windfarm off the coast of south east England were approved by the Government today.

The London Array windfarm, 12 miles off Kent and Essex, will generate enough electricity to power about a million houses - a quarter of all homes in central London.

However, a date for the construction of the £1.5 billion project is unlikely to be set until the outcome of a planning inquiry into the windfarm's electricity substation is known.

David Miliband, the Environment Secretary, said the scheme would help the Government to achieve its target of producing 20 per cent of Britain's electricity from renewable sources by 2020.

The London Array windfarm, approved by the Department of Trade and Industry, will consist of 341 turbines and occupy an area of 90 square miles (232 sq km) between Margate and Clacton. London Array, a consortium of Shell WindEnergy Ltd, E.On UK Renewables and Core Ltd, is behind the 1,000 megawatt project.

A second windfarm, off the coast of Kent, was also given the go-ahead today. The Thanet windfarm will be 7 miles (11km) from North Foreland on the Kent coast and will contain 100 turbines, occupying 13.5 square miles (35 sq km). The £500 million project being developed by Warwick Energy is expected to be completed by 2008. It will supply electricity to around 240,000 homes. The London Array windfarm will supply around 750,000 homes.

Although the London Array windfarm was approved by the DTI, it still needs planning permission for a substation, which would channel the power generated offshore to the national grid.

Planning permission for the substation, at Cleve Hill, Graveney, in Kent, was refused by Swale Borough Council and residents have expressed concern about the rise in the volume of traffic that would be generated during its construction.

London Array has offered an £850,000 community benefits package to appease residents of the village of Graveney including bursaries to local primary and secondary schools, and the offer to fund the higher education costs for one student every year for a decade.

The outcome of the planning inquiry will be announced next year.

Asked if the conflict between the Government and the local council could be resolved through a new planning system, Mr Miliband said: "There are some tricky issues and what I would say is we can’t all be in favour of renewable energy in theory and then against wind turbines in practice."

He added: "We have to change our mindset because climate change does require us to look at these issues in a different way."

Mr Miliband was asked on BBC Radio 4's The World At One programme if the way to balance the conflict was to get people involved in consultation rather than allowing people to object and so delay projects.

He said: "It’s not as simple as that. Even under the present system, as I understand it, the officers in the case of the substation actually recommended in favour of the scheme and there are clear rules that apply, but I think climate change does change the rules of the game and it changes the rules of the game in fundamental ways that require us to think afresh about some of the assumptions that have been held before."

Greenpeace welcomed the Government’s decision.

A spokesman said: "This is one of the most important decisions concerning renewable energy that the Government has had to take. This is clean energy on a massive scale and we have been waiting too long. It’s a pioneering project and we need more of them."

Maria McCaffery , chief executive of the British Wind Energy Association, said: "The significance of these decisions is far greater than the projects themselves, although they will bring many notable benefits to the UK in terms of clean, carbon-free generation.

"Far more important is the clear signal from the UK to the rest of the world that this country is open for business for offshore wind and we look forward to more consents in the near future."

The Royal Society for the Protection of Birds (RSPB) said that London Array was taking into account bird welfare in its construction of the windfarm. The charity raised concerns that the 341-turbine site could threaten the winter colony of around 7,000 rare red-throated divers. The birds are susceptible to disturbance from construction and maintenance work, and the movement of turbines. But the RSPB said it was pleased that the developer would drop plans for additional turbines if the birds were affected by the first stage of the project.

The Government wants to produce 10 per cent of Britain’s electricity from renewable sources by 2010 and it has an aspirational target of 20 per cent by 2020. The current figure is around four or five per cent and the Government estimates that the London Array project will take it another per cent or so towards its target.

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